The present invention refers to a detachable inking device for a flexographic printing machine, its embodiment, cleaning and use in such a machine.
The flexographic printing machines and, more particularly the printing stations of these machines comprise a plate cylinder, a pressure roller, a screened cylinder, commonly called anilox cylinder by the experts, and an inking device. The matter to be printed passes between the plate cylinder and the pressure roller. The screened cylinder, on which ink has been previously applied by the inking device, deposits the ink on the plate cylinder. To obtain four-coulour prints, for example, four printing stations are used, printing each a different colour. The inking devices, being generally used in the printing machines to deposit ink on the screened cylinder, are made up of a chambered doctor blade comprising a chambered doctor blade body on which are mounted two doctor blades coming in contact with the circumference of the screened cylinder. The ends of the chambered doctor blade are sealed by seals. The assembly thus formed constitutes a tank, wherein the ink will be brought, through an inking circuit, by means of a pump. Obviously, the printing machines, to which it is referred here, are adapted to provide a quantity of different printing jobs and in order to do so, all the components of each printing station need to be thoroughly cleaned. This thorough cleaning is relatively easy for components such as the plate cylinder and the screened cylinder but is more difficult as regards the chambered doctor blade which often comprises areas wherein ink residues still remain even after an intensive cleaning.
Each document U.S. Pat. No. 4,590,855, U.S. Pat. No. 5,150,651, EP 0 359 959 B1 and EP 0 611 649 B1 describe an inking devices being similar to the one we have just referred to.
The document U.S. Pat. No. 4,590,855 relates to a chambered doctor blade wherein the doctor blades are mounted on the chambered doctor blade body by means of a small bar holding the doctor blade by means of a hexagon head screw. The tightness of the chambered doctor blade ends is achieved by a seal cut in dependence on the diameter of the screened cylinder. An identical seal is fixed to each end of the chambered doctor blade body my means of a small plate crossed by hexagon head screws ensuring the clamping of the assembly. This chambered doctor blade is arranged so as to be pivotable from a working position against the screened cylinder to a rest position in which it is relatively easy to exchange the used or damaged doctor blades. Obviously, in this position, an additional operation, for example cleaning, can be carried out because of the access to the internal parts of the chambered doctor blade.
The document U.S. Pat. No. 5,150,651 describes a chambered doctor blade wherein the doctor blades are also mounted on the chambered doctor blade body by means of a small bar holding the doctor blade by means of a hexagon head screw. In this embodiment, it has been searched for the possibility of depositing ink in some transverse areas of the screened cylinder. For this purpose, the tightness of these areas, in the chambered doctor blade, is provided by seals which are cut in dependence on the diameter of the screened cylinder and the configuration of the internal part of the chambered doctor blade. Once that these seals are in the required position, they are maintained by the clamping of the doctor blades acting on a part of the seal. This chambered doctor blade is also arranged so as to be pivotable from a working position against the screened cylinder to a rest position in which it is relatively easy to exchange the used or damaged doctor blades and to adjust the position of the seals in the width of the chambered doctor blade. Also obviously, in this position, an additional operation, for example cleaning, can be carried out because of the access to the internal parts of the chambered doctor blade.
The document EP 0 359 959 B1 refers to a doctor blade inking device comprising a chambered doctor blade being detachably fixed on a crossbar which extends parallel to the screened cylinder. The crossbar includes fastenings for fitting or removing of at least one chambered doctor blade on this crossbar. The doctor blades are secured to the chambered doctor blade body in the same manner as has just been described with reference to the two previous patents. The assembly formed by the crossbar and the chambered doctor blade is also pivotable from an operating position to a rest position allowing the same handling operations as those previously cited in relation with the two mentioned U.S. patents.
The document EP 0 611 649 B1 relates to an inking apparatus wherein the doctor blades are held against the chambered doctor blade body by a clamping means comprising levers controlled by cylinders for clamping and loosening the doctor blades. In this device, the doctor blades are of magnetic material, such as a magnet, for temporarily holding the doctor blade against the chambered doctor blade before clamping it by the clamping device. This assembly, as those previously described, is also pivotably mounted in order to be able to carry out operations which are similar to the above-mentioned, this in a rest position.
As will be noted, in all the described devices the fitting and the fixing of the doctor blades achieves by means of clamping means consisting either of screws or of lever and cylinder devices applying their clamping force in punctual manner all along the doctor blade. In one of the cited examples, it has been endeavoured to improve the contact between the doctor blades and the chambered doctor blade body by using a magnetic material for the doctor blades and a ferrous material for the chambered doctor blade body. As has been explained, the inking means need to be thoroughly cleaned at each change of colour of the printing stations. Such a cleaning is also required when replacing a used or damaged doctor blade.
One of the major disadvantages of the devices using punctual clamping means lies in the fact that, when cleaning the chambered doctor blade it always remains ink residues attracted by capillarity between the internal part of the doctor blade and its supporting surface against the chambered doctor blade body. This phenomenon being particularly unpleasant when changing from a dark colour, for example black or blue, to a light colour such as yellow. This lack of cleaning causes a fading of the desired new colour, which is obviously unacceptable.
Another important disadvantage remains in the long time required for exchanging a used or damaged doctor blade, which is essentially due to the tedious removing and refitting of the clamping means of the doctor blades which comprise numerous components. Finally, the chambered doctor blades used in the known devices are of a heavy construction which renders their handling difficult when withdrawing them from the printing machine, which is required, for example for a repair or a thorough cleaning.
The aim of the present invention is to obviate the above-mentioned disadvantages and proposing a detachable inking device comprising an extremely lightweight chambered doctor blade.
For this purpose the inking device according to the invention corresponds to the description of claim 1.